In general, a peristaltic finger pump is used as a liquid transfusion device for an automatic instillation device and is provided between an infusion liquid container such as a pharmaceutical liquid bottle and a body infusion member like an infusion needle as disclosed in the Japanese Laid-Open Patent Publication No. 58-165868. The pump of this type is so constructed that a predetermined quantity of a liquid is transfused by squeezing an elastic liquid transfusion tube in a liquid transfusing direction by movements of a plurality of the finger members. When a clamper and the like disposed in a liquid transfusion tube system to occlude a pharmaceutical liquid fail to open and thereby produce an occluded state for an extended period and a desired quantity of a liquid is not infused, or when a tip of an infusion needle is clogged so that a joint for the liquid transfusion tube is released and when an inner pressure of the liquid transfusion tube is elevated upon release of the clogging with an accidental infusion of the pharmacheutical liquid, which causes trouble. In particular, premature babies and patients in critical condition are subjected to great danger.
Therefore, it has been required to detect such an occlusion of a liquid transfusion tube quickly for prevention of an occurrence of any trouble. There has been a particular apparatus for detecting an occlusion of the liquid transfusion tube to detect an expansion of the transfusion tube due to a variation of a liquid pressure in the liquid transfusion tube by a strain gauge and the like to give an alarm.
However, according to the conventional method of and apparatus for detecting an occlusion of the liquid transfusion tube, the liquid transfusion tube to be detected is required to have an expansion sufficient for detection by a strain guage and the like when an inner pressure is elevated by an occlusion and also to have a constant expansion rate for each liquid transfusion unit, notwithstanding there is no substantial expansion from the spontaneous state even when clogginhg has occurred and also that the conventional apparatus could not be used for the general purpose liquid transfusion unit receiving liquid transfusion tubes of different hardness according to the manufacturers.
The conventional liquid transfusion unit is an istillation liquid transfusion unit manufactured not for use with squeezing by a pump, and since this liquid transfusion unit is free of any squeezing portion for the pump, the structure is simple for mass-production in a single species with the reduced cost.
According to the present invention, when the liquid transfusion tube to be used for the general-purpose liquid transfusion unit is pressurized into a flat shape, the flat portion is sharply displaced against the variation of the liquid pressure in the liquid transfusion tube.